linux-kernel - Re: [PATCH v2 08/21] arm64: KVM: VHE: Introduce unified system register accessors

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Message-ID: <20160201134732.GK1478@cbox>
Date:	Mon, 1 Feb 2016 14:47:32 +0100
From:	Christoffer Dall <christoffer.dall@...aro.org>
To:	Marc Zyngier <marc.zyngier@....com>
Cc:	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will.deacon@....com>,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	kvm@...r.kernel.org, kvmarm@...ts.cs.columbia.edu
Subject: Re: [PATCH v2 08/21] arm64: KVM: VHE: Introduce unified system
 register accessors

On Mon, Jan 25, 2016 at 03:53:42PM +0000, Marc Zyngier wrote:
> VHE brings its own bag of new system registers, or rather system
> register accessors, as it define new ways to access both guest
> and host system registers. For example, from the host:
> 
> - The host TCR_EL2 register is accessed using the TCR_EL1 accessor
> - The guest TCR_EL1 register is accessed using the TCR_EL12 accessor
> 
> Obviously, this is confusing. A way to somehow reduce the complexity
> of writing code for both ARMv8 and ARMv8.1 is to use a set of unified
> accessors that will generate the right sysreg, depending on the mode
> the CPU is running in. For example:
> 
> - read_sysreg_el1(tcr) will use TCR_EL1 on ARMv8, and TCR_EL12 on
>   ARMv8.1 with VHE.
> - read_sysreg_el2(tcr) will use TCR_EL2 on ARMv8, and TCR_EL1 on
>   ARMv8.1 with VHE.
> 
> We end up with three sets of accessors ({read,write}_sysreg_el[012])
> that can be directly used from C code. We take this opportunity to
> also add the definition for the new VHE sysregs.(

weird closing parenthesis.

> 
> Signed-off-by: Marc Zyngier <marc.zyngier@....com>
> ---
>  arch/arm64/kvm/hyp/hyp.h | 72 ++++++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 72 insertions(+)
> 
> diff --git a/arch/arm64/kvm/hyp/hyp.h b/arch/arm64/kvm/hyp/hyp.h
> index fc502f3..744c919 100644
> --- a/arch/arm64/kvm/hyp/hyp.h
> +++ b/arch/arm64/kvm/hyp/hyp.h
> @@ -48,6 +48,78 @@ static inline unsigned long __hyp_kern_va(unsigned long v)
>  
>  #define hyp_kern_va(v) (typeof(v))(__hyp_kern_va((unsigned long)(v)))
>  
> +#define read_sysreg_elx(r,nvh,vh)					\
> +	({								\
> +		u64 reg;						\
> +		asm volatile(ALTERNATIVE("mrs %0, " __stringify(r##nvh),\
> +					 "mrs_s %0, " __stringify(r##vh),\
> +					 ARM64_HAS_VIRT_HOST_EXTN)	\
> +			     : "=r" (reg));				\
> +		reg;							\
> +	})
> +
> +#define write_sysreg_elx(v,r,nvh,vh)					\
> +	do {								\
> +		u64 __val = (u64)(v);					\
> +		asm volatile(ALTERNATIVE("msr " __stringify(r##nvh) ", %x0",\
> +					 "msr_s " __stringify(r##vh) ", %x0",\
> +					 ARM64_HAS_VIRT_HOST_EXTN)	\
> +					 : : "rZ" (__val));		\

what is rZ ?
(complete Google-fu failure misery)

> +	} while (0)
> +
> +/*
> + * Unified accessors for registers that have a different encoding
> + * between VHE and non-VHE. They must be specified without their "ELx"
> + * encoding.
> + */
> +#define read_sysreg_el2(r)						\
> +	({								\
> +		u64 reg;						\
> +		asm volatile(ALTERNATIVE("mrs %0, " __stringify(r##_EL2),\
> +					 "mrs %0, " __stringify(r##_EL1),\
> +					 ARM64_HAS_VIRT_HOST_EXTN)	\
> +			     : "=r" (reg));				\
> +		reg;							\
> +	})
> +
> +#define write_sysreg_el2(v,r)						\
> +	do {								\
> +		u64 __val = (u64)(v);					\
> +		asm volatile(ALTERNATIVE("msr " __stringify(r##_EL2) ", %x0",\
> +					 "msr " __stringify(r##_EL1) ", %x0",\
> +					 ARM64_HAS_VIRT_HOST_EXTN)	\
> +					 : : "rZ" (__val));		\
> +	} while (0)
> +
> +#define read_sysreg_el0(r)	read_sysreg_elx(r, _EL0, _EL02)
> +#define write_sysreg_el0(v,r)	write_sysreg_elx(v, r, _EL0, _EL02)
> +#define read_sysreg_el1(r)	read_sysreg_elx(r, _EL1, _EL12)
> +#define write_sysreg_el1(v,r)	write_sysreg_elx(v, r, _EL1, _EL12)
> +
> +/* The VHE specific system registers and their encoding */
> +#define sctlr_EL12              sys_reg(3, 5, 1, 0, 0)
> +#define cpacr_EL12              sys_reg(3, 5, 1, 0, 2)
> +#define ttbr0_EL12              sys_reg(3, 5, 2, 0, 0)
> +#define ttbr1_EL12              sys_reg(3, 5, 2, 0, 1)
> +#define tcr_EL12                sys_reg(3, 5, 2, 0, 2)
> +#define afsr0_EL12              sys_reg(3, 5, 5, 1, 0)
> +#define afsr1_EL12              sys_reg(3, 5, 5, 1, 1)
> +#define esr_EL12                sys_reg(3, 5, 5, 2, 0)
> +#define far_EL12                sys_reg(3, 5, 6, 0, 0)
> +#define mair_EL12               sys_reg(3, 5, 10, 2, 0)
> +#define amair_EL12              sys_reg(3, 5, 10, 3, 0)
> +#define vbar_EL12               sys_reg(3, 5, 12, 0, 0)
> +#define contextidr_EL12         sys_reg(3, 5, 13, 0, 1)
> +#define cntkctl_EL12            sys_reg(3, 5, 14, 1, 0)
> +#define cntp_tval_EL02          sys_reg(3, 5, 14, 2, 0)
> +#define cntp_ctl_EL02           sys_reg(3, 5, 14, 2, 1)
> +#define cntp_cval_EL02          sys_reg(3, 5, 14, 2, 2)
> +#define cntv_tval_EL02          sys_reg(3, 5, 14, 3, 0)
> +#define cntv_ctl_EL02           sys_reg(3, 5, 14, 3, 1)
> +#define cntv_cval_EL02          sys_reg(3, 5, 14, 3, 2)

as always, fun stuff to review.

> +#define spsr_EL12               sys_reg(3, 5, 4, 0, 0)
> +#define elr_EL12                sys_reg(3, 5, 4, 0, 1)
> +

I couldn't quite decipher the spec as to how these are the right
instruction encodings, so I'm going to trust the testing that this is
done right.

>  /**
>   * hyp_alternate_select - Generates patchable code sequences that are
>   * used to switch between two implementations of a function, depending
> -- 
> 2.1.4
> 

Thanks,
-Christoffer